This disclosure relates generally to a housing and housing system for a substance removing an undesired respiratory gas component of a respiratory gas flow. The housing comprises a first space for receiving the substance, a first wall surrounding part of the first space, a first end operationally connected to the first wall and surrounding part of the first space, the first end comprising a first opening for the gas communication with the first space and a second end opposite the first end operationally connected to the first wall and surrounding part of the first space, the second end comprising a second opening for the gas communication with the first space. The housing also comprises a first channel between the first end and the second end for guiding the gas flow. This disclosure relates also to an arrangement for ventilating lungs of a subject.
Anesthesia machines are optimized for delivering anesthesia to a patient using volatile anesthetic agent liquids. In such systems, the anesthetic agent is vaporized and mixed into the breathing gas stream in a controlled manner to provide a gas mixture for anesthetizing the patient for a surgical operation. The most common volatile anesthetic agents are halogenated hydrocarbon chains, such as halothane, enflurane, isoflurane, sevoflurane and desflurane. Additionally, nitrous oxide (N2O) can be counted in this group of volatile anesthetic agents, although the high vapor pressure of nitrous oxide causes nitrous oxide to vaporize spontaneously in the high pressure gas cylinder, wherefrom it can be directly mixed as gas with oxygen. The anesthetizing potency of nitrous oxide alone is seldom enough to anesthetize a patient and therefore another volatile agent is used to support that.
Since the volatile anesthetic agents are expensive, they are effective greenhouse gases and further harmful to the atmospheric ozone layer, anesthesia machines have been developed to minimize the consumption of the gases. To keep patients anesthetized, a defined brain partial pressure for the anesthetic agent is required. This partial pressure is maintained by keeping the anesthetic agent partial pressure in the lungs adequate. During a steady state, the lung and body partial pressures are equal, and no net exchange of the anesthetic agent occurs between the blood and the lungs. However, to provide oxygen and eliminate carbon dioxide, continuous lung ventilation is required.
Anesthesia machines are designed to provide oxygen to the patient and eliminate carbon dioxide (CO2), while preserving the anesthetic gases. To meet these goals a re-breathing circuit is used. In this patient exhaled gas is reintroduced for inhalation. Before re-inhalation carbon dioxide must be removed from the gas, which is done with a carbon dioxide absorber. Before inhalation, the gas is supplied with additional oxygen and anesthetic agents based upon the patient demand. In this arrangement, the additional gas flow added to the re-breathing circuit can be less than 0.5 L/min although the patient ventilation may be 5-10 L/min. Such ventilation of the lung is carried out using a ventilator pushing inhalation gas with overpressure to patient lungs and then allowing that to flow out passively from the pressurized lungs to the breathing circuit.
Ventilation carries the breathing circuit oxygen to lungs for uptake to be burned in body metabolism. The outcome of this is CO2 that blood circulation transports to lungs wherefrom it becomes carried out with exhalation gas. Before re-inhalation the gas is guided through absorber for CO2 removal. Effective CO2 removal requires close contact with the breathing gas and the removing substance. To provide large contact area, the removing substance is therefore a surface of porous structure of granules that fill the cartridge. The form of this granular structure is guided by the flow resistance, the limitation of which is one key design goals of the breathing circuit. In absorber optimized for minimal resistance the gas flow path through the stacked granules is short and the flow distributes to wide area. In such structure the gas flows slowly because of large surface area providing time for reaction between the gas and absorbent granules.
The absorbers tend to have empty space above the granules. If the gas inlet and outlet to the absorber would be aligned to allow horizontal flow penetration through the cartridge, the flow would favor this empty space and the CO2 would leak through without getting absorbed. Therefore the gas flow must always penetrate through the absorbent on vertical direction.
CO2 absorption takes place in reaction with the absorber. This reaction begins once the CO2 enriched gas flow meets responsive absorbent. Using fresh absorber this occurs on the gas inlet to the absorber. FIG. 1 presents CO2 concentration on the abscissa 1 and absorber height on the ordinate 2. CO2 enriched gas 3 of concentration 4 gets in to the absorber at the top height 5 of the absorbent. When penetrating a distance within the absorbent the concentration reduces as indicated with the graph 6 to zero. Because of the granular structure of the absorbent, this absorption more exactly begins from the layer next to the gas inlet. This vertical height of graph 6 is called transfer zone. The gas CO2 concentration at the beginning of the transfer zone is the inlet concentration and at the end that is zero. Between the transfer zone the concentration declines gradually from inlet concentration to zero. Once the CO2 absorption occurs, the reactive absorbent wears out. As a result of this, the absorption does not occur any more at the inlet, which pushes the transfer zone forward along the gas flow path within the absorber as indicated successive graphs 8, 9, 10.
When the leading edge of the transfer zone reach the other end of the absorber bed 11, with increasing portion the gas flow penetrates through the absorber without the CO2 getting absorbed increasing the CO2 concentration 12 of the gas flowing out from the absorber 13. When the CO2 concentration of the passed gas reach maximum allowed concentration 14, the absorber must be changed. Typically this limit varies between 0.5% to 1%. At this point the absorber has however a lot of remaining absorption capacity left in the transfer zone.
To consume the whole absorption capacity, two absorbers, the first interfacing the breathing circuit and the second interfacing the first absorber, can be connected in series as illustrated on FIG. 2. In these circumstances, when the transfer zone reach the end 15 of the absorber 16, which is uppermost, another fresh absorber 16, which is lower one, in series absorbs the CO2 leaking through when the transfer zone penetrates there. Finally, when the transfer zone reaches the end 15 of the absorber, the absorption capacity of the uppermost absorber 16 has been totally utilized. At this moment the uppermost absorber is discharged, the lower absorber still having remainder capacity is moved to the place of the uppermost absorber, and a new absorber is assigned as the lower absorber.
The use of two absorbers connected in series is well known in anesthesia. This has however been replaced by single absorber cartridges because they allow compact breathing system in having gas inlet port 17 and gas outlet port 18 at one end of the absorber compared to the through-flow of the dual absorber solution where the ports are on opposite ends. This through-flow requires return flow path 19 within the breathing system to re-circulate the CO2 free gases for patient breathing. These channels, as part of the breathing circuit, require regular cleaning, which adds complexity to the anesthesia system maintenance.